Nanostructures formation on surface of 6H-SiC by laser radiation

Formation of nano-structures on a surface of 6H-SiC:N,B and SiC:N under irradiation, by the N-2 pulsed laser was found and studied (wavelength is 337 nm, pulse duration, is 10 ns, energy of pulse is 1.6(.)10(3)J). Formation of the nano-hills is the beginning stage of laser ablation. These nanostructures have shape of a hill and their creation corresponds to the beginning stage of laser ablation. Position of the nano-hills depends on the distribution of intensity of laser radiation. The nano-hills arise along the circular line around the maximum of focussed spot. The threshold intensity of laser rediation for formation of nano-structures is 5GW/cm(2). We propose two models for explanation of the nano-hills formation on the irradiated surface of 6H-SiC based on a liquid phase formation in the bulk of the semiconductor under a thin solid state layer. The results of photoluminescence and morphology by Atomic Force Microscope studies of the irradiated surface allow us to conclude that the concentration of nitrogen atoms increases. The increase of the nitrogen concentration in the hills is explained by presence of the temperature gradient field in the irradiated region of 6H-SiC surface caused by the strongly absorbed laser radiation. According to the Thermogradient effect the N atoms move towards the irradiated surface, while the atoms of B - into the bulk of SiC. As is known the N atoms are donors and the B atoms are acceptors in SiC therefore after cooling of the semiconductor a p-n junction should be created.